Cold storage rooms are in wide spread use for storing, at very low temperatures, various food products. Such cold storage rooms are used in great numbers in the warehousing of frozen foods, and in the storing of frozen foods at grocery stores. Cold storage rooms are well insulated, so that the ceilings, walls and flooring are insulated against the entry of heat energy. Refrigeration apparatus is provided in order to cool the air and the merchandise within the cold storage room.
The cold storage rooms are provided with doors so that personnel and material may enter and leave. It has long been recognized that when the door is opened, warm air is admitted into the cold storage room. This warm air is cooled, and condenses, and would create a lower pressure within the cold storage room than atmospheric. Since the pressure differential tends to cause the cold storage room to collapse inwardly, due to the higher external pressure, such cold storage rooms have been provided with a vent passage, with a valve for admitting air through the passage and into the cold storage room from the exterior, with closing of the valve after the interior pressure has become substantially equal to the outside, atmospheric pressure.
In the construction of cold storage rooms, panels having insulating between the walls are used. As above-noted, a door is provided in an entryway, to provide for ingress and egress. It is now the preferred construction of such cold storage rooms to provide a prefabricated door jamb, including a threshold, and a generally inverted U-shaped structure including a pair of hollow posts, and a connecting hollow transom. The door is mounted to the door jamb structure by hinges, and electrical conduits are enabled to be placed within the door jamb assembly, for such purposes as mounting a light on the door jamb assembly. After construction, foam-in-place pastic is introduced into the interior of the pre-fabricated door jamb.
There have been provided the above-noted pressure relief valves in vent passages in the panels of the cold storage room. The vent passages which have been provided in such installations have been of relatively large construction, and due to the fact that it has been necessary to provide a heater in these passages, in addition to the control valve, it has been necessary to modify the panels to receive electrical conductors to provide energy to the heaters. This has required on-site modification of the panels, at substantial expense in both labor and materials.
Prior art constructions, as disclosed in various United States Patents, have proven deficient. For example, Labahn U.S. Pat. No. 3,813,896 provides an air vent tube through a wall of a walk-in frezer unit having a valve housing outwardly of the exterior wall at the outer end of the tube, containing a pair of valves, the valve elements being ping-pong balls. The positioning of the valve housing is undesirable, and the construction is somewhat expensive, requiring modification of a wall of the walk-in frezer.
Berkowitz U.S. Pat. No. 3,952,542 discloses a large diameter vent passage with dual plate valves in the wall or door of a cold room. A separate electrical junction box is provided, as well as an external conduit for the passage of electrical junction to the connector box.
Cook et al. U.S. Pat. No. 4,257,445 provides a valve construction in the wall of a walk-in refrigerator, and including embodiments with valves with springs, solenoid operated valves, etc. The construction includes, in one embodiment, a heater for a guide rod for a valve element.
Burtis U.S. Pat. No. 3,680,329 discloses a plate valve, pivoted to a support, and carried within a ventilator passage extending through a wall of a refrigerator. A heater is provided in this construction. The assembly is very wide, in comparison to a door of the cold room.
Schmidt U.S. Pat. No. 4,235,162 provides a mounting arrangement for pressure relief valves provided in the cooling rig of a transportation vehicle, the construction including plates providing a labyrynth path.
Kamezaki U.S. Pat. No. 4,116,213 and Kakmezaki U.S. Pat. No. 4,180,093 each discloses a cold storage chamber with a door and air pressure control apparatus in a wall, including pivoted plate valves on the interior and exterior.
In the installation where a vent passage has been provided, it has uniformly been provided in a wall of a cold room or other enclosure, and there has typically been provided a relatively large passage and large valves, with special additional construction for the provision of electrical conductors to supply energy to a heater.